Endometriosis, the abnormal growth of endometrium in ectopic sites, is a serious disease in women that results in severe pain and is often accompanied by infertility. Rhesus and other macaques develop this disease, but studies of the hormonal regulation and properties of endometriotic lesions are complicated by a high degree of variability and extensive adhesions in the pelvic cavity that make sampling and analysis difficult. We have developed a technique for transplantation of endometrium from rhesus monkeys into SCID mice. Such an approach will permit treatment of individual graft-bearing mice as analogs for monkeys and should facilitate analysis of the regulation and properties of ectopic endometrial tissue. Our initial goal was to establish the most appropriate hormonal conditions for transplantation in both donor and host. In our first trials, monkey endometrium was transplanted under hormonal conditions typical of the mid-luteal phase. Pieces of endometrial basalis and functionalis were grafted subcutaneously into spayed SCID mice treated with both E2 and P. Acceptance for basalis was excellent (89 q 4%; n=53), but grafts of functionalis were unsuccessful (0%; n=18). This indicated that the basalis region was the most appropriate region for transplantation. In other trials, the basalis region was grafted immediately after menstruation. This partially models endometriosis as the human disease is presumed to derive from retrograde menstrual flow. In this trial the acceptance rate was 87 q 6% (n=14). In many grafts, the stroma was hypertrophied and the glands were reduced, but immunocytochemical studies showed that regulation of cell proliferation, estrogen and progesterone receptors was normal. These preliminary data indicate that SCID mice will be highly useful in analysis of hormonal control of ectopic endometrial grafts. In the future, we will transplant samples of frankly menstruating endometrium and true endometriotic lesions as we explore the validity of this approach. B3)[unreadable]